Barry's LC Time Simulation

What if you have your capacitor, and know the desired discharge time? This page helps design your coil by telling you the inductance needed for the discharge time. Note this does not include a projectile.

Assumptions

This applet applies to low-resistance circuits. That is, it assumes the discharge is essentially sinusoidal, as is the case with under-damped RLC circuits. A small amount of resistance will not significantly change the timing, as long as R²C² < 4LC.

It solves for time by using the basic equation for time T in an LC resonant circuit:

If your circuit is critically damped or over-damped, don't rely on this applet. Instead, learn more about it by reading my Theory - Damped Oscillator. Better yet, for a timing calculator that handles resistance, see the Magnetic Gun Club - Transient Response page!

LC Time Simulation

This program calculates time by solving the formual (above) for inductance. For example, the zero-crossing formula for inductance in an undamped LC circuit works out to be:

        T2
L = -------------
      pi2 * C 
      

Your goal in this simulator is to choose the inductance. Use this value to design your coil. (Hint: See the next page!)

All You See Is a Big Gray Box?

This program uses Swing and requires Java Runtime Environment (JRE) 1.4 or above.

If you see a red "X", you should update your JRE. You can download it from http://java.sun.com/j2se/1.4.1/download.html and scroll to the section "Download J2SE v 1.4.1_06". Look in the "JRE" column for your own operating system. Download and install the JRE, or if you write Java code then get the software developer's kit (SDK) instead.

If you still see a red "X", then Sun Java may be conflicting with Microsoft JVM. Open "Add/Remove Programs" and remove Microsoft Java Virtual Machine. It is obsolete -- Microsoft has not been maintaining it since Sun had a successful lawsuit against them.

If my applet still doesn't work, open your Java Console window in your web browser. Copy and paste its contents into a message and e-mail it to me for trouble-shooting. The first few lines are especially useful since it identifies your version of Java.

About the Program

The program was written with NetBeans 3.5.1 (www.netbeans.org, a free download) using Swing classes. My Java source code is freely available in these files:

• TimeSim1.java uses a JTable embedded in a JScrollPane to run the user interface
• Nearest.java converts double-precision numbers into engineering notation
• Capacitor.java represents a single capacitor. It has a factory method to deliver an array of industry-standard values
• Inductor.java implements the three different inductance formulas
• For usage examples, you can see how to call the components from my unit test files (based on JUnit).
  TimeSim1Test.java, NearestTest.java, CapacitorTest.java, InductorTest.java

Comments and feature requests are invited! Send them to Barry Hansen.